Alkaline phosphatase

Background

• Group of isoenzymes that catalyzes hydrolysis of organic phosphate esters in the extracellular space
• Found in liver, bone, placenta, ileal mucosa, and kidney
• Can be tissue-specific or tissue-nonspecific, the latter of which makes up most of the serum ALP

Interpretation

• Serum marker from biliary tract, bone, and placenta
• In bone, it indicates high bone turnover, which can be from a number of causes: healing fractures, osteomalacia, hyperparathyroidism, hyperthyroidism, Paget disease of bone, osteogenic sarcoma, and bone metastases
• Hemolysis, jaundice, and high lipids can interfere with testing
• Many things affect serum ALP
  • Decrease serum ALP: clofibrate
  • Increase serum ALP: lots and lots, including verapamil

Isoenzymes

• Electrophoresis can separate into liver, bone, placental, and intestinal fractions
  • Liver and bone are hard to separate